The present disclosure describes interconnect structures. Exemplary embodiments include interconnect structures that can be used for integrated circuits and their assemblies.
An integrated circuit (IC) is a small device with tiny contact pads that must be connected to other circuitry to form a complete system. The interconnection between different ICs or IC assemblies can be done through an interconnect substrate, i.e. a substrate with interconnect lines, e.g. a printed circuit board (PCB) or an interposer. Sometimes, the ICs' contact pads are connected to the substrate's contact pads by metal bond wires: one end of the metal wire is attached to the top surface of the IC, and the other end to the top surface of the substrate (e.g., by melting the end of the metal wire or by ultrasonic bonding). However, to reduce the size of the assembly and shorten the electrical paths, the metal wires can be eliminated: the ICs can be connected to the substrate by flip-chip techniques, i.e., the IC's contact pads can be attached to the substrate's contact pads by solder, adhesive (conductive or anisotropic), or diffusion bonding without the intermediacy of the metal wires.
Sometimes the ICs are stacked on top of each other, and the contact pads of different ICs can be connected together by solder, adhesive, or diffusion bonding as in flip-chip attachment. Such a stack can then be connected to an interconnect substrate. Multiple stacks or IC assemblies can be connected to the substrate to form larger assemblies, which in turn can be connected to other assemblies by similar techniques, possibly using additional substrates.
A challenging situation arises if an assembly includes a stack of ICs or substrates of different lateral sizes; see FIG. 1A, showing three ICs 112.1, 112.2, 112.3 called “die”. (ICs can be manufactured in batch in a semiconductor wafer, which is then cut up to separate the ICs from the wafer; each such IC is called a die or a chip.) The three die are stacked on a substrate 102, and the adjacent die are flip-chip attached to each other, but the top die (112.3) is connected to the substrate by a metal bond wire 114 attached to the top surface of the die and the substrate. In order to shorten this connection, the wire could be replaced by a conductive path passing through the die 112.1 and 112.2 (using through substrate vias (TSVs) for example). However, a simpler solution, eliminating the TSV complexities, is as shown in FIG. 1B, i.e. connect the metal wire 114 to the bottom of die 112.3. This can be done by a process of FIGS. 2A and 2B: first attach the metal wires 114 and die 112.1 and 112.2 (but not 112.3) to substrate 102 as in FIG. 2A, encapsulate the metal wires and the die 112.1 and 112.2 by a molding compound (e.g. epoxy) 128 to stabilize the metal wires 114, and then place the die 112.3 on die 112.2 and the epoxy and bond the die 112.3 to the metal wires 114 as in FIG. 2B. See e.g., FIG. 6 of U.S. Pat. No. 8,618,659 to Sato et al., which patent is incorporated herein by reference herein in its entirety and FIG. 1 of U.S. Pre-Grant Patent Publication No. 2014/0036454 to Caskey et al., which publication is incorporated herein by reference in its entirety.
Bonding the metal wires 114 to the substrate 102 (as in FIG. 1A or 1B) is a lengthy process because the metal wires are attached to the substrate one at a time, as described in U.S. Pre-Grant Patent Publication No. 2013/0313716 to Mohammed, which is incorporated by reference in its entirety. This is especially burdensome for large numbers of metal wires (e.g. hundreds or thousands.)
It is desirable to provide improved processes and materials for forming interconnections.